Myotonic dystrophy type 1 (DM1) is the most common form of muscular dystrophy in adults with an estimated frequency of 1 in 7,500 (Harper P S., Myotonic Dystrophy. London: W.B. Saunders Company; 2001). DM1 is an autosomal dominant disorder caused by expansion of a non-coding CTG repeat in DMPK1. DMPK1 is a gene encoding a cytosolic serine/threonine kinase (Brook J D, et al., Cell., 1992, 68(4):799-808). The physiologic functions and substrates of this kinase have not been fully determined. The expanded CTG repeat is located in the 3′ untranslated region (UTR) of DMPK1. This mutation leads to RNA dominance, a process in which expression of RNA containing an expanded CUG repeat (CUGexp) induces cell dysfunction (Osborne R J and Thornton C A., Human Molecular Genetics., 2006, 15(2): R162-R169).
The DMPK gene normally has 5-37 CTG repeats in the 3′ untranslated region. In myotonic dystrophy type I, this number is significantly expanded and is, for example, in the range of 50 to greater than 3,500 (Harper, Myotonic Dystrophy (Saunders, London, ed.3, 2001); Annu. Rev. Neurosci. 29: 259, 2006; EMBO J. 19: 4439, 2000; Curr Opin Neurol. 20: 572, 2007).
The CUGexp tract interacts with RNA binding proteins including muscleblind-like (MBNL) protein, a splicing factor, and causes the mutant transcript to be retained in nuclear foci. The toxicity of this RNA stems from sequestration of RNA binding proteins and activation of signaling pathways. Studies in animal models have shown that phenotypes of DM1 can be reversed if toxicity of CUGexp RNA is reduced (Wheeler T M, et al., Science., 2009, 325(5938):336-339; Mulders S A, et al., Proc Natl Acad Sci USA., 2009, 106(33):13915-13920).
In DM1, skeletal muscle is the most severely affected tissue, but the disease also has important effects on cardiac and smooth muscle, ocular lens, and brain. The cranial, distal limb, and diaphragm muscles are preferentially affected. Manual dexterity is compromised early, which causes several decades of severe disability. The median age at death is 55 years, usually from respiratory failure (de Die-Smulders C E, et al., Brain., 1998, 121(Pt 8):1557-1563).
Antisense technology is emerging as an effective means for modulating expression of certain gene products and may therefore prove to be uniquely useful in a number of therapeutic, diagnostic, and research applications for the modulation of DMPK1. Intramuscular injection of fully modified oligonucleotides targeting with the CAG-repeat were shown in mice to block formation of CUGexp-MBNL1 complexes, disperse nuclear foci of CUGexp transcripts, enhance the nucleocytoplasmic transport and translation of CUGexp transcripts, release MBNL proteins to the nucleoplasm, normalize alternative splicing of MBNL-dependent exons, and eliminate myotonia in CUGexp-expressing transgenic mice (Wheeler T M, et al., Science., 2009, 325(5938):336-339; WO2008/036406).
Presently there is no treatment that can modify the course of DM1. The burden of disease, therefore, is significant. It is, therefore, an object herein to provide compounds, compositions, and methods for treating DM1